I know the bridge you talk about very well. The minimum clearance at the highest high tide is about 27ft average is about 30ft. My trimaran
is fitted with a tabernackle system that was done by a local guy about six years ago but from what I hear he is no longer doing that kind of work. I can ask the PO what it cost but I think the fitting was somewhere around $5k. It is a rather simple system, but I will warn you it is a lot of work and half the time limited our usage of the boat. It may sound like a rather simple task but when you add on the regular work required to either get a boat underway or pack it up and stow everything afterwards it because quite a bit of work.
As to what is required, the mast
will be unstepped and you will need to have a new mast step fabricated and installed, you will also need to cut off a small portion of the front foot of the mast in order for it to tabernackle. Once that is done you will need to replace a few of the shroud
turnbuckles with quick release latches
as well as the rear stay. And if you go with the same method we use which uses the main sheet for all the heavy lifting you will need to purchase
a much longer main sheet which will need to be thicker than what you have and probably be a cored line. Ours I would say is close to 100ft in total length which for a replacement costs around $2-3/ft.
Keep in mind I am talking about a 38ft trimaran
with a 43ft mast that probably weighs somewhere in the thousands of pounds with full rigging
attached which puts our mast head
somewhere around 52-55ft off the water
. If you have a much smaller boat it would obviously be substantially easier.
If you want I would be happy to meet you some day and show you our tabernackle system. We are now moored on the otherside of the bridge and get a lot more usage out of the boat since we can simply throw off the dock
lines and come and go whenever we please with little additional effort.